Cosmology

Abstract:

The intrinsic alignment of galaxy shapes (by means of their angular momentum) and their cross-correlation with the surrounding dark matter tidal field are investigated using the 160 000, z = 1.2 synthetic galaxies extracted from the high-resolution cosmological hydrodynamical simulation HORIZON-AGN. One- and two-point statistics of the spin of the stellar component are measured as a function of mass and colour. For the low-mass galaxies, this spin is locally aligned with the tidal field ‘filamentary’ direction while, for the high-mass galaxies, it is perpendicular to both filaments and walls. The bluest galaxies of our synthetic catalogue are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to ∼10 h^{− 1} Mpc comoving distance. We also report a correlation of the projected ellipticities of blue, intermediate-mass galaxies on a similar scale at a level of 10⁻⁴ which could be a concern for cosmic shear measurements. We do not report any measurable intrinsic alignments of the reddest galaxies of our sample. This work is a first step towards the use of very realistic catalogue of synthetic galaxies to evaluate the contamination of weak lensing measurement by the intrinsic galactic alignments.

Abstract:

We present an analysis of the diffuse emission at 5 GHz in the first quadrant of the Galactic plane using two months of preliminary intensity data taken with the C-Band All-Sky Survey (C-BASS) northern instrument at the Owens Valley Radio Observatory, California. Combining C-BASS maps with ancillary data tomake temperature-temperature plots, we find synchrotron spectral indices of β = -2.65 ± 0.05 between 0.408 and 5 GHz and β = -2.72 ± 0.09 between 1.420 and 5 GHz for -10° > |b| > -4°, 20° > l > 40°. Through the subtraction of a radio recombination line free-free template, we determine the synchrotron spectral index in the Galactic plane (|b|>4°) to be β =-2.56±0.07 between 0.408 and 5 GHz, with a contribution of 53±8 per cent from free-free emission at 5 GHz. These results are consistent with previous low-frequency measurements in the Galactic plane. By including C-BASS data in spectral fits, we demonstrate the presence of anomalous microwave emission (AME) associated with the HII complexes W43, W44 and W47 near 30 GHz, at 4.4Σ, 3.1Σ and 2.5Σ, respectively. The CORNISH (Co-Ordinated Radio 'N' Infrared Survey for High mass star formation) VLA 5-GHz source catalogue rules out the possibility that the excess emission detected around 30 GHz may be due to ultracompact HII regions. Diffuse AME was also identified at a 4Σ level within 30° > l > 40°, -2° > b > 2° between 5 and 22.8 GHz.

Abstract:

We present numerical simulations of a 15 M_⊙ star in a suite of idealized environments in order to quantify the amount of energy transmitted to the interstellar medium (ISM). We include models of stellar winds, UV photoionization and the subsequent supernova based on theoretical models and observations of stellar evolution. The system is simulated in 3D using RAMSES-RT, an Adaptive Mesh Refinement Radiation Hydrodynamics code. We find that stellar winds have a negligible impact on the system owing to their relatively low luminosity compared to the other processes. The main impact of photoionization is to reduce the density of the medium into which the supernova explodes, reducing the rate of radiative cooling of the subsequent supernova. Finally, we present a grid of models quantifying the energy and momentum of the system that can be used to motivate simulations of feedback in the ISM unable to fully resolve the processes discussed in this work.

Abstract:

Measuring radio source counts is critical for characterizing new extragalactic populations, brings a wealth of science within reach and will inform forecasts for SKA and its pathfinders. Yet there is currently great debate (and few measurements) about the behaviour of the 1.4-GHz counts in the microJy regime. One way to push the counts to these levels is via 'stacking', the covariance of a map with a catalogue at higher resolution and (often) a different wavelength. For the first time, we cast stacking in a fully bayesian framework, applying it to (i) the SKADS simulation and (ii) VLA data stacked at the positions of sources from the VIDEO survey. In the former case, the algorithm recovers the counts correctly when applied to the catalogue, but is biased high when confusion comes into play. This needs to be accounted for in the analysis of data from any relatively-low-resolution SKA pathfinders. For the latter case, the observed radio source counts remain flat below the 5-sigma level of 85 microJy as far as 40 microJy, then fall off earlier than the flux hinted at by the SKADS simulations and a recent P(D) analysis (which is the only other measurement from the literature at these flux-density levels, itself extrapolated in frequency). Division into galaxy type via spectral-energy distribution reveals that normal spiral galaxies dominate the counts at these fluxes.